Candidate of technical science, associate professor of MAMI, Director of the department of magnetic separators (Russia)
There is a fallacious approach to analyze potential efficiency of various magnetic separators — evaluating them by field intensity rate H (induction rate B) on the surface of a magnet taken apart from the system, or local magnetic intensity rate in most «magnetico-active» areas of a magnetic precipitation element. As a result, the preference is given to a device with higher rates.
We would like to draw your attention to the fact that the described argumentation is of deliberately advertising nature. In fact, there are two factors to be taken into consideration by the customer.
First. Besides the declared filed local intensity rate H (induction rate B) you should know topography H (or B) all over the working surface of a magnetic separator, that is, in any point where filtrated medium goes. As a rule, out of the advertised local zones the named rates are intolerably low.
Second. In the final account there is a more objective characteristic to estimate potential magnetic sorption, besides field intensity rate H (induction rate B), and it is called magnetic force factor. It is calculated as H·gradH, where gradH is level of field nonuniformity. This leads us straight to a conclusion, that even if H rate in the separator is very high, up to hyper-values, but gradH remains low, the product H·gradH is also low which means that filtering potential of a separator is minimal.
For example, analyzing the potential of popular grate separators considering magnetic force factor, it becomes clear that using round rods considerably restricts the flow area, and as thus, resistance to medium flow increases. Because of this fact, separator becomes cluttered from time to time and the technological process breaks down. Then either the gap between magnetic rods should be increased (this leads to reduction or even lack of magnetic force factor between the rods) or the separator's productivity should be limited or the separator size should be larger. Very often the choice is to increase the gap between the rods, thus creating a two-stage or even multiple-stage separator variant. Opposite rods then are placed in staggered rows to ensure covering active and passive zones. However, this involves rise in price for the construction and, still, implies intolerable increase of resistance to filtered medium flow.
We have developed and recommend magnetic separators with flat magnetic rods. Due to this construction medium chocking under filtration is prevented while branched magnetic flows cover the whole space between adjoining rods, that is, the whole of the filtered medium passing between them.